On Tue, Mar 03, 2020 at 09:09:38AM -0800, Andrii Nakryiko wrote:
> On Tue, Mar 3, 2020 at 6:12 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > hi,
> > for bpftrace I'd like to print BTF functions (BTF_KIND_FUNC)
> > declarations together with their names.
> >
> > I saw we have btf_dump__emit_type_decl and added BTF_KIND_FUNC,
> > where it seemed to be missing, so it prints out something now
> > (not sure it's the right fix though).
> >
> > Anyway, would you be ok with adding some flag/bool to struct
> > btf_dump_emit_type_decl_opts, so I could get output like:
> >
> > kfunc:ksys_readahead(int fd, long long int offset, long unsigned int count) = ssize_t
> > kfunc:ksys_read(unsigned int fd, char buf, long unsigned int count) = size_t
> >
> > ... to be able to the arguments and return type separated,
> > so I could easily get to something like above?
> >
> > Current interface is just vfprintf callback and I'm not sure
> > I can rely that it will allywas be called with same arguments,
> > like having separated calls for parsed atoms like 'return type',
> > '(', ')', '(', 'arg type', 'arg name', ...
> >
> > I'm open to any suggestion ;-)
>
> Hey Jiri!
>
> Can you please elaborate on the use case and problem you are trying to solve?
>
> I think we can (and probably even should) add such option and support
> to dump functions, but whatever we do it should be a valid C syntax
> and should be compilable.
> Example above:
>
> kfunc:ksys_read(unsigned int fd, char buf, long unsigned int count) = size_t
>
> Is this really the syntax you need to get? I think btf_dump, when
> (optionally) emitting function declaration, will have to emit that
> particular one as:
>
> size_t ksys_read(unsigned int fd, char buf, long unsigned int count);
>
> But I'd like to hear the use case before we add this. Thanks!
the use case is just for the 'bpftrace -l' output, which displays
the probe names that could be used.. for kernel BTF kernel functions
it's 'kfunc:function(args)'
software:task-clock:
hardware:backend-stalls:
hardware:branch-instructions:
...
tracepoint:kvmmmu:kvm_mmu_pagetable_walk
tracepoint:kvmmmu:kvm_mmu_paging_element
...
kprobe:console_on_rootfs
kprobe:trace_initcall_start_cb
kprobe:run_init_process
kprobe:try_to_run_init_process
...
kfunc:x86_reserve_hardware
kfunc:hw_perf_lbr_event_destroy
kfunc:x86_perf_event_update
I dont want to print the return type as is in C, because it would
mess up the whole output, hence the '= <return type>'
kfunc:ksys_readahead(int fd, long long int offset, long unsigned int count) = ssize_t
kfunc:ksys_read(unsigned int fd, char buf, long unsigned int count) = size_t
also possible only in verbose mode ;-)
the final shape of the format will be decided in a bpftrace review,
but in any case I think I'll need some way to get these bits:
<args> <return type>
thanks,
jirka
